Typically, superconducting magnets, such as those used in a magnetic resonance imaging system, are fully filled with liquid helium at the manufacturing facility. After being filled with the liquid helium, the superconducting magnet is ramped-up and tested to ensure that it performs according to its specifications. Then the magnet is shipped to an imaging site where it will be installed.
Liquid helium works well as a coolant for very low temperature applications, but it has a low boiling point. Once the magnet has been installed, a coldhead with a compressor is utilized to keep the loss of liquid helium due to evaporation to a minimum. The coldhead and compressor require a power supply in order to function. Typically, when a superconducting magnet is being shipped, a sufficient power supply is not available. Therefore, during a long shipment, the magnet may lose a significant percentage of the liquid helium used as a coolant. For example, one conventional design uses approximately 2000 liters of liquid helium and it is common to lose up to 1000 liters of liquid helium from the time the superconducting magnet leaves the factory until it is installed.
In order to avoid damaging the magnet, it is necessary to fully fill the superconducting magnet with liquid helium prior to ramping the superconducting magnet to its operational level at the installation site. Liquid helium is expensive and the process of adding liquid helium to compensate for losses incurred during shipping adds extra time and cost to the installation process for superconducting magnets. Therefore, there is a need for a more efficient and less expensive way to manage the liquid helium level in superconducting magnets.